Yes, crossing was extremely hazardous - especially during the early years of the war. It was, of course, during that period that the men of the our engineer units were shipping over to N. Africa.
The convoy in your story was lucky, however, many lost many ships against wolfpacks. Convoy SC-7 lost 20 ships to seven U-boats; 7 to Otto Kretschmer's U-99 alone. Fortunately, Allied ASW techniques improved all the while we were reading their ever-so-breakable unbreakable Enigma code.
One thing I find interesting is the fact that for all of their effort and advanced technology, the Germans' U-boots faired rather poorly after the first few years of the war. The Americans in the Pacific, however, ate the Japanese lunch. Although the US sunk less tonnage than the Germans (5.3 mil Gross Ton. vice 14.5) the US had much greater success per boat. The Germans lost 783 boats (around 30,000 men!) while sinking 3500 ships (around 4 sinkings per u-boat.) The US lost 52 boats (3,506 men) while sinking 1,392 Japanese vessels (26 per sub average!)
Here is a good U-boot site:
http://www.uboat.net/index.html
The US Navy has a lot of good info on US boats.
http://www.navy.mil/navydata/cno/n87/history.html
